The investigations proposed for the entire project period are designed to examine in detail, the nature of host-virus interactions and the relationship of other host factors to the development of bronchial hyperreactivity and reactive airway disease (RAD) in early childhood. Studies have been outlined to characterize the specific immunologic mechanisms in the respiratory tract and the role of common respiratory viral infections and viral specific immune responses in the etiology and pathogenesis of RAD in infancy and childhood. It has been proposed to examine a) the spectrum of viral infections in the human respiratory tract, the nature of infection induced immune responses relative to the development of RAD, b) the role of bronchiolitis acquired in early infancy in the development of bronchial asthma in later life, and c) the role of the common respiratory viral infections in provoking bronchial hyperreactivity in patients with established RAD.